Glucose is an important source of energy to the cells in the human body and abundantly present in food ingredients. After consumption of starch or other dietetic available sources of glucose and their subsequent digestion, glucose is released in the gastrointestinal tract, where it is rapidly and effectively absorbed from the intestinal lumen. This will usually increase glucose concentrations in blood. The change in glucose after consumption of a food is called the postprandial glucose response (PPGR), which can be measured as the area under the curve (AUC) which plots the plasma glucose concentration with time. The human body strives to maintain homeostasis of glucose levels in tissue and blood with time, in order to allow proper functioning of all cells. One important instrument to achieve glucose homeostasis is the release of insulin by the pancreas when the concentration of specific food components like glucose starts to increase. Under normal circumstances this will increase glucose transport into the cell and the formation of glycogen using glucose, and trigger other metabolic changes, therewith rapidly causing the blood glucose levels to decrease to normal levels.
A person that does not react properly on released insulin is said to be insulin-resistant. Large groups of persons suffer from insulin resistance like many obese persons, persons suffering from the so called metabolic syndrome (or syndrome X), diabetics and many patients in hospitals or nursing homes who developed a temporarily or longer lasting insulin resistance as a cause of their disease. Part of the diabetics also experience an insufficient capacity to increase insulin concentrations in blood after consumption of food (called post-prandially). Persons that suffer from insulin-resistance demonstrate abnormal high postprandial glucose response, even after consumption of moderate amounts of food ingredients that comprise glucose. When high postprandial glucose concentrations occur relatively frequently and over longer periods of time, they can cause several severe health problems. Known secondary side effects, as can be found in diabetics, are problems in the cardiovascular system, such as hypertension, atherosclerosis, bad blood supply to peripheral tissues, stroke, heart attacks etc., as well as problems in the kidney, in particular an abnormal glomerular filtration rate, and a wide range of neuropathies and retinopathies like cataract. It was also found that mortality of severe disease in hospital patients is associated with the severity of insulin resistance.
The decrease of postprandial glucose response (PPGR) has been the subject of numerous research efforts. Many types of carbohydrates have been proposed to induce a low PPGR. Also inclusion of dietetic fibre in a nutritional product has been proposed for this purpose, for example viscous fibres, like gums or pectin. The disadvantage of using such fibres is the increase in viscosity when used in liquid products in amounts that are effective. According to the European FLAIR Concerted Action on Resistant Starch (EURESTA) resistant starch is defined as “the sum of starch and products of starch hydrolysis not absorbed in the small intestine of healthy individuals”.
Commercially available ingredients that can be used as a source of resistant starch are mainly considered to be a source of fibre, so being non-digestible, thereby neglecting the value of the remaining digestible part of the ingredient as a principle source of digestible carbohydrates. It is generally avoided to include fibres in Western nutritional food products in amounts larger than 20-40 grams per daily dose, as they are believed to cause gastrointestinal discomfort in these doses, like bloating, flatulence and loss of appetite. Patients in hospitals or nursing homes may also develop constipation or a high faecal mass when too high amounts or the wrong type of fibres are consumed, especially in combination with drinking too little. In liquid enteral nutrition for the latter group of patients typically about 1 g fibres is included in a nutritional product per 20 g digestible carbohydrates.
Englyst H. N. et al., Eur. J. Clin. Nutr., 46, Suppl. 2, S33-S50 (1992), classify resistant starch (RS) into three categories for reasons of different digestion resistance: Type 1 RS are starches which are physically inaccessible to the digestive enzymes, type 2 RS are starches that exist as granules and can comprise predominantly amylose, and type 3 RS are retrograded starches. Cross-linked and/or chemically modified starches are sometimes considered to be type 4 RS, but their non-food grade status makes them at present undesirable for commercial application in the food industry.
Each of these ingredients can be manufactured differently and their behaviour in vivo depends on the way the ingredient was processed, prior to consumption. Typically manufacturers of resistant starch ingredients develop an ingredient having a RS level that is as high as possible and this amount must be constant and independent of the way of processing of the ingredient when it is included in new food products.
It is known that the digestibility of native starch can change during food processing, especially when heat is applied to the food carbohydrates. Heat treatment plays an important role in manufacturing of clinical liquid formulae, in order to kill micro-organisms or spores thereof and thereby make the formulae safe for consumption by persons that suffer from disease or health disorders or persons who are immune-compromised and/or to prevent spoilage of the formulae during shelf life. A heat treatment may have different effects on the starch properties, as does moisture content, pressure, pH, ionic strength, during processing and in the nutritional product. Annison G. and Topping D. L., Ann. Rev. Nutr. 1994, 14, 297-320, show a significant increase of the viscosity of a starch-containing nutrition when subjected to a specific heat treatment, and even gelatinization may occur, which is undesirable in liquid clinical nutritional products that are intended to be used for tube—or sip-feeding. In addition, the starches may crystallize and precipitate in production lines or in the product, therewith causing problems with homogeneity and blockage of tubing lines. Starch crystals may cause a sandy feeling in the mouth, when consumed.
In the art little attention is paid to the fraction of resistant starch ingredients that is actually available in vivo to man. Most commercially available RS ingredients are to a varying degree partially digestible within 20 minutes after consumption. The remainder is undigested by the enzymes that are released within the human gastrointestinal tract and used as fermentable substrate by colonic micro-organisms. Therefore such resistant starch ingredients do not behave as sustained release carbohydrates.
For example, EP-A-1.088.832 discloses a granular starch that is prepared by selected heat-moisture treatment and which heat-treated starch is made resistant for more than 80%, preferably has a molecular weight of 5-20 kDa (degree of polymerization (DP) of 30-123) and a low amylopectin content. The material is appreciated as source of dietary fibre. Food products are described which comprise more than 20 wt % of total dietary fibre. EP-A-0846704 describes a retrograded starch having more than 55% resistant starch with more than 50% of linear chains of α-glucans having a DP between 10-35 and a DSC melting peak temperature below 115° C. It is suitable for use as a prebiotic component, in particular as a butyrate-producing fibre.
A starch having sustained digestion properties is taught in US 2003/0219520. The enzymatically debranched starch comprises at least 90% linear α-glucans, preferably a highly crystalline amylose having 6-65 anhydro-glucose units linked by α-1,4-D-glucoside bonds and a DE>6.0. No change in the material properties is observed during typical food processing conditions, when included in an amount of 1-50 wt % in a wide range of food products. Upon consumption, between 22 and 50 wt % is digested in the first twenty minutes, and 48-74 wt % is digested within two hours, after start of the test. Table 2 demonstrates the digestibility profile after a specific heat treatment at high or low moisture results: about 31-40% is digested during the first 20 minutes and 65-70% during the first 120 minutes after start of their test. The document is silent about the behaviour of the ingredient, when it is subjected to heating at higher temperatures and in particular ultra high heat treatments, as can be beneficially used during manufacture of enteral clinical nutrition. It is also silent about the effect of heating in a matrix that comprises proteins and/or lipids and/or other carbohydrate fractions. These components are known to be able to interact with amylose crystallization and therewith digestibility.
It is therefore an object of the invention to provide a nutritional product that is heat-treated and safe with regard to the presence of micro organisms, spores and other potentially harmful components, that is attractive to the consumer from an organoleptic point of view, especially in terms of mouth feel of the product when it is stored for prolonged times, and that is extremely effective in providing rapidly glucose to the consumer and maintaining a clinically significant supply of glucose during a prolonged time without resulting in undesirably high concentrations of glucose in the blood, even in persons that have become insulin resistant.
It is a further object of the invention to provide such products to persons that suffer from insulin resistance in order to prevent development of disorders which result from prolonged and frequent high levels of glucose in blood, such as those diseases that result from advanced glycation products (AGE), neuropathies, retina problems, and kidney problems.